Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention relates to a process for the preparation of a mixture of glucosylmannitol and glucosylsorbitol by the hydrogenation of glucosylglucosone.
The invention relates in particular to a process for the preparation of a mixture of glucosylmannitol and glucosylsorbitol by the hydrogenation of glucosylglucosone, in the presence of a catalyst, using specific hydrogenation pressure and temperature conditions for a high glucosylglucosone solids content.
The present invention relates more precisely to a process for the preparation of a mixture of glucosylmannitol and glucosylsorbitol by the continuous hydrogenation of glucosylglucosone in a fixed catalyst bed, and more particularly to the implementation of this continuous process in a succession of fixed catalyst beds arranged in series and in at least two reaction zones.
Finally, the present invention relates to a mixture of glucosylmannitol and glucosylsorbitol, especially a mixture of xcex1-1,4-linked or xcex1-1,6-linked isomers of glucosylmannitol and glucosylsorbitol, containing at least an equimolar proportion of glucosylmannitol and glucosylsorbitol.
2. Description of the Prior Art
These mixtures of xcex1-1,4-linked or xcex1-1,6-linked isomers are conventionally prepared either by mixing each of the two components in the desired proportions or by isomerizing or epimerizing specific disaccharides.
Thus glucosyl-xcex1-1,4-mannitol and glucosyl-xcex1-1,4-sorbitol (or maltitol) can be produced separately and then combined to give the expected mixture.
However, although maltitol is easy to prepare by hydrogenating a maltose syrup obtained from a starch hydrolyzate by any means conventionally known to those skilled in the art, glucosyl-xcex1-1,4-mannitol is prepared by a step involving isolation of the rare sugar glycosyl-xcex1-1,4-mannose from complex media (extracts of algae or yeasts, for example) by expensive and complex processes with very low yields, followed by a hydrogenation step.
As regards the xcex1-1,6-linked isomers, the corresponding mixture of the two components glucosylmannitol and glucosylsorbitol in equimolar proportions is known to those skilled in the art by the name palatinitol.
Palatinitol is a low-calorie bulk sweetener with a low cariogenicity; it is obtained e.g. by the catalytic hydrogenation of isomaltulose, or glucosyl-xcex1-1,6-fructose, at neutral pH.
Isomaltulose itself is obtained by the enzymatic isomerization of sucrose, or glucosyl-xcex1-1,2-fructose, with the aid of a sucrose glycosyltransferase.
Among other documents relating to the preparation and properties of palatinitol, reference may be made to the book xe2x80x9cAlternative Sweetenersxe2x80x9d published in 1986 by LYN O""BRIEN NABORS, chap. 11, pp. 217-244.
However, this isomerization process only affords a roughly equimolar mixture of glucosyl-xcex1-1,6-mannitol and glucosyl-xcex1-1,6-sorbitol (or isomaltitol) without the possibility of varying the relative composition of the two constituents in the mixture.
In patent applications WO 97/19093 and WO 97/19094, of which the Applicant is the proprietor, it was shown that palatinitol could also be prepared from isomaltose, or glucosyl-xcex1-1,6-glucose.
Isomaltose in turn is prepared from glucose or a maize syrup as described for example in patent application FR 2.515.186.
However, although these alternative processes make it possible to obtain palatinitol without being obliged to use sucrose as the starting material, it is nevertheless the case that this mixture of glucosyl-xcex1-1,6-mannitol and glucosyl-xcex1-1,6-sorbitol can still only be obtained in equimolar proportions.
At best the final mixture can contain a high proportion of glucosyl-xcex1-1,6-sorbitol if the chromatography techniques normally employed in the processes of patent applications WO 97/19093 and WO 97/19094 for separating the components of said mixture to give an equimolar mixture are not used.
Also, the mixture can advantageously be enriched in isomaltitol simply by adding said compound obtained elsewhere by the catalytic hydrogenation of isomaltose.
It is apparent from all the above that there is an unsatisfied need for a simple process which makes it possible in the vast majority of cases to obtain a mixture of glucosylmannitol and glucosylsorbitol, irrespective of the type of linkage isomer in question, in at least equimolar proportions and, more particularly, enriched in its glucosylmannitol component.
Anxious to develop a process which makes it possible to meet practical constraints better than the processes already in existence, the Applicant found that this objective could be achieved by a process for the catalytic hydrogenation of glucosylglucosone carried out under specific temperature and pressure conditions.
xe2x80x9cGlucosonexe2x80x9d, also known as 2-ketoglucose or D-arabino-2-hexulosone, is understood as meaning the product resulting from the chemical treatment of glucose with hydrogen peroxide or with copper acetate or, advantageously, the product resulting from the enzymatic conversion of glucose with the aid of a pyranose-2-oxidase.
It is further known in the state of the art that pyranose-2-oxidase also has a broad spectrum of enzymatic modification.
Thus, in Med. Fac. Landbouww. Univ. Gent., 62/4a, 1997, pp. 1193-1197, HUWIG et al. show that pyranose-2-oxidase isolated from Peniophora gigantea is capable of reacting with isomaltose to give the oxidation product of its glucose in the terminal reducing position, i.e. glucosyl-xcex1-1,6-glucosone.
Likewise, in Arch. Microbiol., 1997, 167, pp. 119-125, VOLC et al. show that pyranose-2-oxidase isolated from Agaricus bisporus reacts with maltose to give glucosyl-xcex1-1,4-glucosone.
However, nowhere do these documents describe or suggest that it is possible advantageously to use these two xcex1-1,4-linked and xcex1-1,6-linked isomers of glucosylglucosone to give, by means of a specific hydrogenation process, a mixture of glucosylmannitol and glucosylsorbitol in at least equimolar proportions, and more particularly at mixture containing a high proportion of glucosylmannitol preferably equal to at least 1.5.
To its credit the Applicant therefore found a process for the preparation of a mixture of glucosylmannitol and glucosylsorbitol which is characterized in that glucosylglucosone is hydrogenated, in the presence of a catalyst, by subjecting a glucosylglucosone solution with a solids content equal to at least 10% by weight, preferably of between 20 and 50% by weight, to a pressure equal to at least 30 bar, preferably of between 30 and 200 bar, and to a temperature equal to at least 50xc2x0 C., preferably of between 50 and 150xc2x0 C.
In this way the Applicant found that the process according to the invention makes it possible to hydrogenate the xcex1-1,4-linked and xcex1-1,6-linked isomers of glucosylglucosone equally well.
The process according to the invention uses a glucosylglucosone solution with a solids content equal to at least 10% by weight, preferably of between 20 and 50% by weight.
Glucosylglucosone of very high purity, advantageously produced from maltose or isomaltose enzymatically by any means known per se to those skilled in the art, is chosen for the preparation of the solution to be hydrogenated. The choice of the xcex1-1,4-linked or xcex1-1,6-linked isomer of glucosylglucosone as the starting material to be hydrogenated is then based on the nature of the mixture of glucosylmannitol and glucosylsorbitol which it desired to obtain.
xe2x80x9cHigh purityxe2x80x9d is understood as meaning a glucosylglucosone content in the order of 100%.
The catalyst is selected from the group consisting of palladium, nickel, ruthenium, platinum, rhodium, cobalt, copper, zinc, chromium, manganese and tungsten and is preferably nickel.
In one preferred embodiment of the process according to the invention, in which the catalyst is suspended in the glucosylglucosone solution to be hydrogenated, it is advantageous to choose nickel in its form known as Raney Ni.
In another preferred embodiment of the process according to the invention, the catalyst can be impregnated or co-exchanged on an inert support preferably selected from the group consisting of active charcoal, peat, zeolites, aluminosilicates and titanium dioxide. It preferably consists of active charcoal.
The weight ratio catalyst/inert support is advantageously set at a value of between 1 and 5%, preferably in the order of 2%.
It is also possible to use a catalyst containing a promoter. This promoter can be selected from the group consisting of titanium, molybdenum and platinum.
In one embodiment of the process according to the invention, a suspension of glucosylglucosone with a solids content of between 10 and 50% is prepared and the catalyst is introduced in its Raney Ni form.
In this case it is chosen to use a hydrogenation pressure equal to at least 30 bar, preferably of between 30 and 200 bar and particularly preferably in the order of 100 bar, and a temperature equal to at least 50xc2x0 C., preferably of between 50 and 150xc2x0 C. and particularly preferably a temperature in the order of 125xc2x0 C.
The pressure conditions are generally chosen to substantially avoid hydrolysis, even partial hydrolysis, of the glucosylglucosone to glucose and glucosone, which is likely to result in the appearance of fructose, sorbitol or mannitol in the final mixture of glucosylmannitol and glucosylsorbitol.
In another embodiment of the process according to the invention, it is chosen to carry out the hydrogenation in a continuous mode on a fixed catalyst bed.
In this case the catalyst is arranged in a fixed bed in the form of a compact stack of particles, the whole being placed on supporting grids in a hydrogenation reactor. It is advantageous to choose a trickle-flow reactor.
In terms of the invention, xe2x80x9ctrickle-flow reactorxe2x80x9d is understood as meaning a hydrogenation reactor in which a liquid phase, containing the product to be hydrogenated, and a gas phase circulate in co-current or counter-current, preferably in co-current from top to bottom, through a fixed bed of catalyst particles in which the hydrogenation reaction takes place.
The flow rates of these two phases are regulated so as to allow the liquid to trickle over said catalyst particles and ensure the best contact between the two liquid and gaseous phases on the one hand and the solid catalyst phase on the other.
In one embodiment of the process according to the invention, it is chosen to prepare a fixed bed consisting of 200 l of commercial catalyst, the chosen value of the feed rate of the glucosylglucosone solution with a solids content of between 10 and 50% by weight is between 150 and 250 kg/h and the chosen amount of hydrogen introduced into said trickle-flow reactor is in the order of two to fifteen times the stoichiometry of the reaction.
In this case the hydrogenation pressure and temperature used are advantageously chosen to have respective values in the order of 30 to 150 bar, for example 150 bar, and in the order of 50 to 150xc2x0 C., for example 90xc2x0 C.
The mixture of glucosylmannitol and glucosylsorbitol is then obtained in equimolar proportions and with a conversion yield equal to at least 90%.
In one preferred embodiment of the process according to the invention, it is chosen to carry out a continuous process for the hydrogenation of glucosylglucosone in a succession of fixed catalyst beds arranged in series and in at least two reaction zones.
In this case the hydrogenation is advantageously carried out in a first reaction zone, consisting of at least one fixed catalyst bed, to give a high conversion of the glucosylglucosone to a mixture of glucosylmannose, glucosylfructose and glucosylglucose containing a high proportion of glucosylmannose, and then in a second reaction zone, consisting of at least one fixed catalyst bed, in which hydrogenation is carried out to give a mixture of glucosylmannitol and glucosylsorbitol with a high degree of conversion and a high proportion of glucosylmannitol.
The Applicant thus found that it is possible to carry out the hydrogenation in a continuous mode and in at least two reaction zones, so as to separate the step involving the production of the mixture of glucosylmannose, glucosylfructose and glucosylglucose from the step involving the production of the mixture of glucosylmannitol and glucosylsorbitol, to give the mixture of glucosylmannitol and glucosylsorbitol with a high glucosylmannitol content never previously achieved, and with a high productivity and a high degree of conversion.
It is possible to use different kinds of catalyst in each of the reaction zones, but it is preferred to use the same kind of catalyst in both these zones.
In the first reaction zone, the pressure conditions are regulated so as to give a high conversion, equal to at least 80%, of glucosylglucosone to a mixture of glucosylmannose, glucosylfructose and glucosylglucose containing a high proportion of glucosylmannose.
In terms of the invention, xe2x80x9chigh proportion of glucosylmannosexe2x80x9d is understood as meaning a glucosylmannose content equal to at least 40% by weight, preferably equal to at least 70% by weight of the mixture.
The hydrogenation pressure in the first reaction zone is set at a value equal to at least 50 bar and of between 50 and 100 bar, preferably in the order of 80 bar.
In the second reaction zone, the pressure conditions are regulated so as to give the mixture of glucosylmannitol and glucosylsorbitol, containing a high proportion of glucosylmannitol, with a degree of conversion equal to at least 95%.
In terms of the invention, xe2x80x9chigh proportion of glucosylmannitolxe2x80x9d is understood as meaning a weight ratio glucosylmannitol/glucosylsorbitol equal to at least 1.5.
The hydrogenation pressure in the second reaction zone is set at a value equal to at least 100 bar and of between 100 and 200 bar, preferably in the order of 150 bar.
The hydrogenation temperature is preferably kept constant in the two reaction zones at a value of between 50 and 100xc2x0 C. and in the order of 90xc2x0 C., as exemplified below.
The fixed catalyst beds are advantageously arranged in trickle-flow reactors. It is chosen to use 200 l of commercial catalyst particles, the chosen value of the feed rate of the glucosylglucosone solution with a solids content of between 10 and 50% by weight is between 200 and 300 kg/h and the chosen amount of hydrogen is between two and fifteen times the stoichiometry of the reaction.